1. Field of the Invention
The present invention relates to a system for driving a motor, and more particularly relates to a system for driving a motor by employing chopper control.
2. Description of the Prior Art
There are three types of DC motors, i.e., a series motor, a shunt motor and a compound motor. Up to the present, a series motor has been mainly used for applications such as electric trains, where the speed control is necessary, because of the ease of control and the cost and volume of the chopper apparatus. However, as the magnetic fields of a series motor must be switched in accordance with the rotational speed range of the motor, the structure of the motor is complicated and problems such as limitation of the torque in the high speed range and the difficulty of the regenerative control are unavoidable. Therefore, the type of the motor for such application has been gradually switched over to a shunt motor or a compound motor recently. However, in the case of a shunt motor, the ratio of the current fluctuation against the voltage fluctuation is relatively large so that it is a problem how the influence of the voltage fluctuation can be suppressed.